Fuel cells have been proposed as a power source for electric vehicles and other applications. One known fuel cell is the PEM (i.e., Proton Exchange Membrane) fuel cell that includes a so-called “membrane electrode assembly” (MEA) comprising a thin, solid polymer membrane-electrolyte having an anode on one face of the membrane-electrolyte and a cathode on the opposite face of the membrane-electrolyte. A polymer selected for use as a PEM desirably has unique characteristics including permeability to protons and electrical insulation. In practice, polymers that fulfill these requirements tend to be relatively fragile and thin, with a typical thickness of approximately 10 to 125 μm. When adding the electrodes to the PEM to form the MEA, the PEM is subjected to relatively high stress conditions including both high temperature and pressure. Since the PEM membrane is fragile, it is handled and processed carefully to minimize physical tears or thinning.
The MEA is sandwiched between a pair of electrically conductive porous fluid distribution media layers. The MEA together with the fluid distribution elements form a compliant layer, which is then sandwiched between a pair of electrically conductive contact elements (generally called bipolar or separator plates) that serve as current collectors for the anode and cathode, and further often contain appropriate channels and openings for distributing the fuel cell's gaseous reactants (i.e., H2 & O2/air) over the surfaces of the respective anode and cathode.
Diffusion media are typically made from fibers (preferably carbon or graphite fibers) or metals, such as foams or screens. Such diffusion media generally has the potential for manufacturing flaws, including small protrusions (such as protruding fibers) that may potentially cause damage to the MEA. Further, separator plate contact with adjacent elements is achieved by the application of compressive force, and must be optimized to enhance fuel cell operation without causing damage to the MEA. Overall, the associated components and assembly contacting the MEA can lead to excessive wear and strain, shortening the lifespan of the fuel cell. There is a need for a protective layer to cushion the MEA, while not detracting from electrical performance of the fuel cell, nor adding excessive cost to the fabrication of the fuel cell. There remains the challenge to optimize fuel cells, including the diffusion media elements and assemblies made therefrom in a fuel cell to promote efficiency, electrical conductivity, and MEA durability as cost-effectively as possible.